AFAIK, it was a 'proposal' that came from some of the Ubi devs on the SH5 project (who were on good terms with the Subsim community),
I get the impression that after they approached the individual modders, they then presented their proposal to the legal & management folks, and somewhere along that road, it got shot down.
Got to see it from their point of view I suppose, collaberating with uncontracted, unpaid & unmanaged volenteers, outside of the controlled development enviroment. Thats got to be a legal & logistical minefield for a big fish like Ubisoft, who want to do everything by the book.
It was a nice idea with the best of intentions, but one it seems, that was never actually going to be allowed to happen.
Maybe if SH5 had been produced by someone like Valve (in the late 90's), it might have been different.